One of the greatest challenges facing humanity is global climate change, i.e. the overheating of the Earth's surface caused by greenhouse gas emissions, the most important of which is carbon dioxide (CO2).
Any combustion leads to emissions of this gas, whose molecules have the property of absorbing and emitting the infrared radiation that our planet sends out. This back-and-forth energy between the Earth's surface and the atmosphere has caused our planet's average surface temperature to rise by 1,2°C above pre-industrial levels.
With the Paris Agreement of 2015, it was established that the temperature of the globe should never exceed 2 ºC over the next few decades and that, preferably, it should not exceed 1,5 ºC.
This last objective is today practically impossible to assess by the content of the last report, the sixth, of the IPCC - Intergovernmental Panel on Climate Change, of the United Nations (the documents of the IPCC working groups are already available on the Internet since last year) .
What can be done to stop climate change? The answer is simple, although its realization is very difficult.
CO2 emissions have been rising. They need to decrease. We have to emit less CO2, preferably none, or better, balance any emissions with absorptions in order to obtain a zero net result (net zero). The various countries are voluntarily making promises of reduction: Portugal promised net zero for the year 2050.
The energy sector is one of the biggest emitters of CO2. We need energy for transport, for industry, commerce and agriculture, etc. and, to obtain this energy, we are still very dependent on fossil fuels (oil, natural gas and coal).
The climate challenge is, to a large extent, that of switching from these energy sources, which cause emissions, to alternative sources (hydroelectric, wind, biomass, solar, geothermal and nuclear energy), which do not cause or cause much less.
It is urgent, in addition to saving energy, to abandon fossil energies. There is a variety of technologies available, but it is not easy to make the «energy transition», not least because wind and solar energy are dependent on meteorological conditions that are not always met, and it is not easy to store the energy produced.
Let's look at the Portuguese case. In Pordata, which compiles data from official sources, primary energy consumption is indicated. The good news is that since 2000, we have been using less energy: in 2000 we consumed 25.254 thousand tons of oil equivalent (toe) and in 2021 only 20.817.
But the bad news is that most of the energy we use is still linked to fossil fuels: in the year 2021, oil accounts for 8456 thousand toe (41% of the total) and natural gas for 4974 thousand toe ( 24%). Coal is practically residual among us today and that's just as well because this is the fuel with the most emissions.
Renewable energy amounts to 6585 thousand tons (32%).
We see that there is still a long way to go for the country to reduce the consumption of fossil fuels, which continue to be necessary in transport and industry. The current situation is weighing on the country's economy, since oil and natural gas are purchased abroad.
The situation is better if we only look at electricity production. We are not self-sufficient in this production: in recent years we have imported electricity.
In 2021, 50.968 gigawatt hours of electricity were produced among us (the gigawatt hour, GW h, is a unit of energy; 1 toe = 11,63 MW h). There were 33,093 GWh of renewable energies, which makes up 65% of the total electricity production, a very good fraction.
Ahead of renewable energies is hydroelectric energy (13.455 GW h), followed very closely by wind (13.216 GW h): each of them represents about 26% of total electrical energy.
There is still to add biomass (4007 GW h), photovoltaic (2237 GW h) and geothermal (179 GW h), the latter only with expression in the Azores.
The time evolution of the energy used is a good indicator of our energy transition: in the year 2000, renewable energies were only 30% of electrical energy, but the proportion has risen since 2018 consistently above 50%.
It is forecast to continue to rise in order to meet the net zero target. Wind energy has the potential to grow if generating units are placed in offshore areas (there is a project for the area off the coast of Figueira da Foz) and the same happens with photovoltaic energy, given the country's solar energy.
On the international scene, Portugal is well placed. According to a 2021 ranking by Enerdata (a French energy sector consultancy), Norway leads with 99% renewable energy from electrical production, followed by New Zealand (81%) and Brazil (78%). Portugal occupies an honorable 7th place, just behind Sweden. The country is on the right track...
Carlos Fiolhais is a Physicist and Science Communicator
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